1. Field of the Invention
The invention relates to a method of generating X-ray images by means of a photoconductor which is provided on a conductive substrate and whose surface potential can be read by means of probes, and also relates to a device suitable for carrying out such a method.
2. Description of the Related Art
A method and device of this kind are known from the publication "Proceedings of SPIE", Vol. 626, 1986, pp. 176-184 as well as from DE-OS 40 04 348 which corresponds to U.S. Pat. No. 5,097,493. Therein, the surface potential of the surface potential of the photoconductor is read by means of a probe device. The probes could be situated at different distances from the surface of the photoconductor and these distances could fluctuate during the reading of the photoconductor. If no steps are taken, this will cause artifacts in the X-ray image reconstructed by means of the image data supplied by the probes. To this end, during the read-out operation the distance between the probes and the surface of the photoconductor is continuously determined by applying an alternating voltage to the substrate. This alternating voltage is capacitively applied to the probes which thus supply an alternating voltage signal whose amplitude is a measure of the probe distance.
In the method described in "Proceedings of SPIE", supra, the dependency on distance of the amplitude of the alternating voltage is utilized to generate correction data which is applied to the image data so as to compensate for the distance fluctuations and to suppress the associated artefacts. In the method described in DE-OS 40 04 348, however, the probes are moved in the direction perpendicular to the photoconductor in dependence on the signal amplitudes measured so that the distance remains substantially constant.
In order to avoid mutual influencing of the image signals on the one hand and the alternating voltage signals on the other hand, the frequency of the alternating voltage must be substantially higher than that of the image signals. Therefore, the image signals and the alternating voltage are separated and processed in two channels by suitable filters.